0
$\begingroup$

I'm having some issues with special relativity. I must misunderstand something but i'm not sure what. I would very much appreciate your help.

We can see from time dilation, if you are traveling with the speed of light, your time freezes compared to stationary outside observers. After one second in the speed of light frame, should take infinite time in the stationary frame.

However when the sun sends a photon towards earth, when the photon reaches earth the earth should be long gone, because infinite time has passed?

I would love to hear what you think.

$\endgroup$
  • $\begingroup$ "After one second in the speed of light frame, should take infinite time in the stationary frame." - please take the time to do a search on this site for this frequently asked question and see that the problem lies with the bolded phrase in the quote. $\endgroup$ – Hal Hollis Jun 12 '18 at 17:17
  • $\begingroup$ "We can see from time dilation, if you are traveling with the speed of light, your time freezes compared to stationary outside observers. After one second in the speed of light frame, should take infinite time in the stationary frame." The passage of time is not affected for you if you are traveling with a speed close to the speed of light. Time for you will pass at the same rate no matter how fast you're going. It's the outside observer who will calculate that your clock ticks slower, but you will calculate the same thing for him. $\endgroup$ – Andrei Geanta Jun 12 '18 at 17:19
  • $\begingroup$ "After one second in the speed of light frame, should take infinite time in the stationary frame. However when the sun sends a photon towards earth, when the photon reaches earth the earth should be long gone, because infinite time has passed?." Photons do not have a well-defined frame of reference, so it's meaningless to talk about how they experience time. They are massless - so they are constrained to always move at the speed of light - they cannot ever be at rest. $\endgroup$ – Andrei Geanta Jun 12 '18 at 17:25
  • $\begingroup$ The answers are fine, but if you want to look at your logic there is also a mistake in how you are perceiving "an infinite amount of time". If it takes an infinite amount of time for something to happen, that means things aren't happening. So if the photon sees that things on earth take "an infinite amount of time" to occur, then this means that things are moving extremely slowly. You are viewing infinite time as just everything has already occurred, which is not the case when the time between events are "infinitely long" $\endgroup$ – Aaron Stevens Jun 12 '18 at 18:03
1
$\begingroup$

I think where you are going wrong is "your time freezes".

What this means is that if you have a clock on your hand, you will see your own clock tick normally (whatever speed you move with), but far away observers will see your clock on your hand to tick slowly.

In your case, the EM wave traveling from the Sun will travel the Sun Earth distance in approx 8 minutes seen from Earth (on a clock on Earth). Now you could ask, but how much time passed on the EM wave's clock. Now the problem is, as per SR, you cannot ask that question, because EM waves do not have an inertial reference frame. Nothing with rest mass can travel with speed c. But theoretically you could say that the EM wave's clock stopped (as seen from Earth).

Now you could ask what neutrinos' clocks coming from the Sun will show. You will still see approx 8 minutes pass seen from Earth (on a clock on Earth) until the neutrino gets here. But if you were traveling with the neutrino, you would see your clock tick normally, but only a fraction of that time would pass on your clock until you would get here.

The problem is you think the way around, you think that normal spatial speeds are the ones we are experiencing. That is not right, because the normal speed is the speed of light, and everything is relative to that.

Anything without rest mass always moves in space with that speed. In the time dimension that particle is not moving. To start moving in the time dimension and start experiencing time like we do, you need to gain rest mass. Now it is because the universe is set up so that the 4 speed vector (x,y,z,t) has a magnitude always c. Now if you slow down in the spatial dimensions (by gaining rest mass), to compensate, your speed in the time dimension will start to change. You will start moving in the time dimension.

$\endgroup$
  • $\begingroup$ I see. Thank you for taking the time to explain that to me. $\endgroup$ – Pernk Dernets Jun 12 '18 at 19:37
1
$\begingroup$

Unfortunately you can not move at the speed of light. There is no well-defined reference frame and you can't talk about "being" in that frame.

We can't talk about what the photon experiences because it is not defined.

$\endgroup$
  • $\begingroup$ Thank you for the comment. But, what if we are at the limit of the speed of light instead - and we fly from the sun to the earth. Would the earth still be there? $\endgroup$ – Pernk Dernets Jun 12 '18 at 17:46
  • $\begingroup$ @pernkDernets look at my comment on your question. If we are traveling near the speed of light then we will observe the Earth's time as very slow (very close to your "infinite time". So if 10 years pass for us we might only see 1 second pass on Earth. Us observing an "infinite amount" of time between events on Earth (in our frame) does not mean the Earth will experience an infinite amount of time (in its frame). $\endgroup$ – Aaron Stevens Jun 12 '18 at 18:07
0
$\begingroup$

The answers above Pretty much sum up everything. Additionally, I also want to say that light would not even experience time. As you also can't Speed anything up to the Speed of light or personally accelerate to that Speed, it is indeed not realistic to answer this Question. That is because in the real world it is impossible.

The Speed of light is just the maximum Speed Limit of our universe, it is absolute, unlike our reference Frames or those of muons for example. So, everyone will measure c as being approximately 300.000km/s and I think a Photon measuring its distance wouldn't even make sense. I hope I could help you in a way!

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.